Ensuring reliability and validity for essay questions

The situation is not always so bleak. For example, in the 1985–87 period, the virtual synchrony model was proposed and emerged as a widely adopted standard (it was used in the Isis Toolkit, Horus, Transis, Ensemble, Totem, Spread , C-Ensemble, Phoenix and Quicksilver systems, and is the basis for the CORBA fault-tolerant computing standard; the model is also used in IBM Websphere to replicate business logic and in Microsoft's Windows Server 2008 enterprise clustering technology). Virtual synchrony permits a multi-primary approach in which a group of processes cooperate to parallelize some aspects of request processing. The scheme can only be used for some forms of in-memory data, but when feasible, provides linear speedups in the size of the group.